1. Field of the Invention
The present invention pertains to automatic test systems and more particularly to integrity determination of the connection between individual telephone subscribers and a four wire switching system.
2. Description of the Prior Art
Each subscriber of a telephone switching system is connected to that system by two wires, termed tip and ring. Switching systems typically these two wires in order to terminate them to the called subscriber's line. As long as the gain or loss along the loop connection from one subscriber to another is minimal, the two wire switching configuration will provide adequate transmission capability. However, when the gain or loss exceeds a threshold limit, amplification of the voice signals is necessary. An example of the gain/loss problem is a long distance telephone call.
A solution to the problem is to amplify each talking path, that is, from the first subscriber to the second subscriber and from the second subscriber to the first subscriber. Therefore, each transmission path requires two wires for amplification and each switching system must have the capability to switch four wires instead of merely two wires.
Four wire switching capability is also required within a digital switching system. Since PCM signals are transmitted by a digital switching system, two wires are required for each talking path as mentioned above.
Conversion apparatus is required to connect the four wire switching path to the telephone subscriber's two wire path. This conversion apparatus is a two wire to four wire hybrid network. This hybrid network is a balancing network with compensating networks connected to maintain the balance of the two wire to four wire connection. Any manipulation of the telephone subscriber's terminal equipment (eg. telephone handset) or change in the length or quality of the subscriber's loop connection affects the delicate balance of the hybrid network.
As the length of the telephone subscriber's loop changes or the type of line changes, the compensation networks must be altered to maintain the balance of the hybrid network.
Historically, the procedure for keeping each subscriber's line balance was a multi-step manual procedure. First, the load of the subscriber's two wire connection pair or cable must be dynamically measured. This measurement changes with the location of the subscriber equipment or the type of line. Second, a repairman would locate the subscriber's line circuit connection within the switching equipment. Next, the repairman must locate the hybrid circuit associated with this line and determine which type of compensation network is presently connected to the hybrid network.
Next, the repairman must open circuit the telephone subscriber's line and check the hybird network and compensation network through the switching system. The repairman must reestablish the telephone subscriber's connection to the system and compare the compensation network which is presently connected to the hybrid with the value obtained via his measurement. He then must make any alteration of networks, that may be required.
This procedure must be performed for each subscriber line. Furthermore, the procedure must be performed at periodic intervals for the entire switching system.
U.S. Pat. No. 4,139,745, issued on Feb. 13, 1979, to G. R. Ashdown et al, teaches a computer controlled test system only for detecting the load presently existing on a cable connecting the subscriber to the switching system.
Accordingly, it is the object of the present invention to provide an automated apparatus for controlling and indicating the integrity of the connection of a telephone subscriber's line to a four wire switching system.
It is a further object of the present invention to provide such an apparatus for use in monitoring each of the subscribers in a telephone switching office.
It is another object of the present invention to provide the mentioned service in an efficient and economical manner.
It is yet another object of the present invention to provide an automated system for periodically checking and controlling the proper connection of compensation networks to a hybrid network.